Quatech RS-422/485, MPA-200/300 user manual DCE Configuration

10.2 DCE Configuration

On the MPA-200, the difference between the DTE and DCE signals is that, with the exception of a few control signals, the pins used for signal transmission on the DTE are used for signal reception on the DCE and vice versa. For example, pin 2 of the DCE connector is received data, yet the corresponding DTE signal is the transmitted data. This allows the user to connect a DTE device to a DCE device and perform communication without the use of any customized cable or adapter.

The control signals that the DCE can generate are the Clear to Send (CTS), Carrier Detect (CD), and Data Set Ready (DSR). It can receive the signals Data Terminal Ready (DTR) and Ready to Send (RTS). All of the control signals are controlled through channel A of the SCC, with the exception of the CD signal, which is generated on channel B.

Depending on the value of TCKEN (D2 of the communications register) the DCE’s transmit clock (TCLK from the SCC ‘s TRXCA pin) can either be trans- mitted on TTCLK, or not used at all because the DCE can not receive a TCLK. Depending on the value of RCKEN (D3 of the communications register), the DCE’s receive clock (RCLK from the SCC’s RTXC pins) can either be received on RRCLK or generated on TRXCB of the SCC. In this second case, the signal from TRXCB is also transmitted on RTCLK. Figure 5 illustrates the clock circuitry of the MPA-200 for its DCE configuration.

27 Quatech Inc., MPA-200/300 Manual